This invention is an improvement of my earlier invention described in United States Patent No. 4,798,364 which provides a novel and unique way of making and using a plywood form liner which is rigid and easy to handle as well as eliminating edge leakage even though the form liner may be reused a considerable number of times.
In using the reinforced form liner which is described and claimed in my above-identified patent, it has been found that the heat which is generated during the setting of the concrete after it has been poured into the forms causes the relatively thick fluted portions of the elastomeric concrete form liner to expand and contract at different rates across the cross section of the liner. Because of the mass of the elastomeric material which is present within the form liner, especially those which are used to texture the outer surface of the finished concrete, the expansion and contraction of the various portions the liner causes the final shape of the set concrete to take on an hourglass appearance. Thus when looking at a cross section of the elastomeric form liner, especially those that produce an elongated parallel ridge and valley configuration in the concrete surface, the portion of the liner which produces the valleys in the finished configuration contain a large mass of elastomeric material. On the other hand, the thin web between these portions which form the ridge in the concrete surface is relatively thin in comparison and thus has a different dimensional expansion or contraction when placed in use.
It is believed that the reinforcing sheet which is molded to the back of the elastomeric concrete liner in the present invention helps to minimize the expansion and contraction movement of the liner, but movement still takes place especially in the area of the elastomer located furthest away from the reinforcing sheet.
In addition, because of the density of the elastomeric material which is used in this type of product the reinforced concrete liner is quite heavy which makes it more difficult to handle by construction workers. As a result, it is desirable to reduce the amount of elastomeric material which is utilized in the construction of the reinforced form liner and thus in turn reduce the overall weight of the finished liner and eliminate the expansion problem. It has been found that the inclusion of stabilizing strips usually fabricated from wood within the fluted area of the reinforced concrete form not only reduces the weight of the finished form, but reduces the amount of elastomeric material that is used in the molding of the liner so that the actual thickness of the elastomeric material whether it is in the web area or in the fluted area is essentially the same. Thus, the expansion problem that exists with the prior art form liners can be essentially eliminated with the arrangement which is provided in the present application.
Another problem that has existed in the prior art is the method which has been used in the past to attach the flexible concrete liner to the forms and the necessity for using whalers, stringers or strengtheners on the outside of the form structure to provide vertical and horizontal strength to support the weight of the concrete. At the present time in many cases, the flexible concrete form liner used with conventional forms is glued to plywood sheeting which forms the back of the form. In the novel concrete form liner which is described in my above-identified patent the elastomeric liner material which contains the texture for the face of the finished concrete is molded and adhered directly to the plywood backing sheet during the molding process. The elastomeric material provided around the outside edges of the plywood sheet also provides a watertight seal around the outside edges which prevents loss of water from the concrete after it has been placed in the form so that complete bonding of the concrete will take place during the setting process.
An object of the present invention is to provide wooden reinforcing strips embedded within the elastomeric material as a base for nailing or fastening the conventional elastomeric form liner to a form plywood sheet. In this way, the elastomeric liner can be removed if and when it is desired which is impossible if the liner has been glued or molded permanently to the backing sheet.
A problem also has been found when using premolded elastomeric form liners in the field. When it is necessary to cut the form liner to custom fit a particular area in the construction, the elastomeric material especially in an area having a large mass causes a hand saw or an electric rotary or saber saw to bind, making it difficult to cut the material especially on a curved line. It is felt that the inclusion of cuttable stabilizing strips embedded in the elastomeric material especially when the strips are made from wood greatly reduces or eliminates this problem. The presence of the wood within the form liner apparently allows the saw teeth to clear themselves from the elastomeric material to greatly reduce the binding of the saw blade.